1. Field of the Invention
The present invention relates to a lithographic apparatus and a device manufacturing method.
2. Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. The lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs), flat panel displays, and other devices involving fine structures. In a conventional lithographic apparatus, a patterning means, that is alternatively referred to as a mask or a reticle, can be used to generate a circuit pattern corresponding to an individual layer of the IC (or other device), and this pattern can be imaged onto a target portion (e.g., comprising part of one or several dies) on a substrate (e.g., a silicon wafer or glass plate) that has a layer of radiation sensitive material (e.g., resist). Instead of a mask, the patterning means can comprise an array of individually controllable elements that generate the circuit pattern.
In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic apparatus include steppers, in that each target portion is irradiated by exposing an entire pattern onto the target portion in one go, and scanners, in that each target portion is irradiated by scanning the pattern through the beam in a given direction (the “scanning” direction), while synchronously scanning the substrate parallel or ant parallel to this direction.
In lithographic apparatus, components that generate heat can introduce into the apparatus positional errors between components due to thermal expansion. This, in turn reduces the accuracy of the images generated by the lithographic apparatus. Accordingly, it is desirable to minimize the generation of heat by components within the lithographic apparatus.
Known arrays of individually controllable elements contain of the order of two million or more individually controllable elements. Each element is provided with a control signal in order to control the element and heat is generated both by the provision of the control signal and by the switching of the individually controllable element between two states. Accordingly, although the heat to be dissipated for each individually controllable element can be small, overall there can be a significant amount of heat to be dissipated from an array of individually controllable elements. Furthermore, the generation of heat within the array of individually controllable elements is dependent of the pattern formed. Therefore, unlike many other components within a lithographic apparatus, the heat generation within an array of individually controllable elements is not constant.
Therefore, what is needed is a system and method to manage heat generated in arrays of individually controllable elements, such that impact on imaging capability caused by such heat generation is substantially reduced.